Remove sequential_promise_test helper, just use promise_test

LayoutTests/resources/testharness-helpers.js

Index: LayoutTests/resources/testharness-helpers.js
diff --git a/LayoutTests/resources/testharness-helpers.js b/LayoutTests/resources/testharness-helpers.js
index b71b2494ec6d427d2608a506df2740bc77b23c45..4d7af1ff9ca77c85696f35368ff3a7a1c4b2480b 100644
--- a/LayoutTests/resources/testharness-helpers.js
+++ b/LayoutTests/resources/testharness-helpers.js
@@ -161,23 +161,3 @@ function stringifyDOMObject(object)
     }
     return JSON.stringify(deepCopy(object));
 }
-
-(function() {
-  var promise_tests = Promise.resolve();
-  // Helper function to run promise tests one after the other.
-  // TODO(ortuno): Remove once https://github.com/w3c/testharness.js/pull/115/files
-  // gets through.
-  function sequential_promise_test(func, name) {
-    var test = async_test(name);
-    promise_tests = promise_tests.then(function() {
-      return test.step(func, test, test);
-    }).then(function() {
-      test.done();
-    }).catch(test.step_func(function(value) {
-      // step_func catches the error again so the error doesn't propagate.
-      throw value;
-    }));
-  }
-
-  self.sequential_promise_test = sequential_promise_test;
-})();